Wave transmission system



Jan. 7, 1930.

E. v. GRiGGs 1,742,909

WAVE TRANSMISSION SYSTEM I I Original Filed Feb. 17 1 922 2 Sheets-Sheet l 0-200- &

fie; Cid/yer wx/zra/i/c 6e/7e/z7/m Hmerk'n'gqs Patented Jan. 7, 1930 V UNITED STATES PATENT OFFICE mums v. caress, or warm PLAINS, NEW YORK, Assmnon 'r o wns'rnnn mnc'rmc COMPANY,INCOBPOBATED, OF NEW YORK, N. Y., A CORPORATION 01 NEW YORK i TRANSMISSION SYSTEM Original application flied February 17, 1922,

' 1925. Divided and This invention relates to wave transmis: sion systems and has for an object the control of theenergy level of transmissionin such systems. v

5 This application is a division of original a plication Serial No. 537,156, filed February 17,1922, entitled Wave transmission s stems. This became Patent 1,565,091, ecember 8, 1925.

The inventionis capable of use in various types of signaling'sy'stems where it is desired to control the energy level of transmission.- It is particularly useful, for example, in stabilizing the transmision characteristics of wave transmission systems employing a wide range of frequencies.

t is well known that in systems of this type changes in the attenuation of the transmission medium produce corresponding variations in the overall transmission equivalent of the system, and result in large fluctuations in the volume of a telephone or other message being transmitted. g

In order to overcome the efiects of transmission variations in such systems, it is common practice to subject a pilot current to the same conditions as those affecting the signaling currents, and to utilize the pilot current so transmitted to adjust an element in the transmission line at various points in the system. Such a system oftransmission control is shown, for example, in Patent Noi 1,511,013

to H. A. Affel, is sued October 7, 1924;

According to;a feature of the present invention, a pilot current is transmitted between the terminals of a wave transmission system over a pilot line the attenuation of which varies in thesame manner as that of the main transmission line. At the distant terminal the pilot current causes the amplifying factor of an amplifier in the receiving circuit to vary gradually and continuously in such manner as to compensate for attenuation variations of the line.

For the purpose of illustration the invention will be described in connection with the particular type of wave transmission system described in the above mentioned parent application, Serial No. 537,156, filed February 50 17, 1922 (Patent 1,565,091). In telephone I the receiving terminal may Serial No. 537,156. ratent No. 1,565,091,. time December a, this application filed lugnst 8,

1925. Serial no. 48,943.

transmission systems of'that type the dis tance to which a'wide range'of essential frequencies may be transmitted over certain circuits, such as submarine cables, is limited because of the diflerence in transmission of the various frequency components involved. -In

order to overcome'this difiiculty means are provided for efiectively reducing the frequencies' of the various componentsof a band of waves so as to make them fall within the transmission range of commercial transmisg sion circuits. This is accomplished, inaparticular embodiment of that invention, b subands dividing speech into narrow 'frequenc and transmitting each band at ow requencies over a separate cable or other circuit. In 7 order to insure that the fre uency increase at e the same as the fre uencv reduction at the transmittting terminal the fre uency changing wavesat both terminals are erived from a common source. More specifically, a base frequency wave .is

transmitted from the common source,and the fre uency changing waves are derived from the ase frequency wave'by harmonic. genera- Incarrying outthe-present invention, the base frequency wave which is emplo ed to control the frequency changing opera ion at the transmitting "and receiving terminals is 'also utilized to determine the operation of thelgain control apparatus. In one embodiment of the inventlon separate gain control devices are associated with the several cable circuits and are all controlled in accordance with the received pilot wave to regulate the gain or amplification of thesubbands incoming over the respective circuits. It will be understood, of course, that the gain control system of this invention may also be em- 'ployed in connection with various other types of transmission systems.

In the drawings, Figs. 1 and 2, when placed side by side with Fig. 1 at the left illustrate the invention as appli d-to a telephone system arranged for multiple circuit submarine cable operation. I

In the drawing, a telephonev line 101 terminating at station X is shown connected with a distant telephone line 102 terminating return .an

' maybe placed in individual'cables or may all at stationY bfi means of cable circuits 103, 104, 105, etc. y way-of example, it may be assumed that these circuits have such transmission characteristics that each of them may be dependent upon this transmission range and will increase as the ractical transmission band of each circuit decreases. The cable circuits ma be metallic or may be'fgro'und (l the drawing is intended to ind c'ate diagrammatically either ty e of circuit. Moreover, the conductors of t ese circuits be placed in the same cable, depending upon circumstances. The latter form of construction is preferable from the standpoint of economy in first cost wherever it is P8111118- sible from the standpoint of transmission reuirements. Each of these cables may be of t e periodically loaded (Pupin) or cont1nuous y loaded (Krarup) types. Attenuation equalizers may also be employed ,to counter-' act the effect of different line attenuations for different frequency components by giving such attenuation to eachcomponent that the added attenuations caused by the line and the equalizer are the same for eachcomponent, Various attenuation equalizer circuits are well 'known. Although any desirable typemay be used, that preferred in this system and illustrated is of the typedisclosed in Figs. 9 and 10 of U. S. patent to Hoyt, N 0. 1,453,980, dated May 1, 1923; Its advantage as an el e-- ment of a' system in which filters are employed is obvious. It is'to be understood that the various receivin circuit devices referred to herein as band lte rs comprise not only freuency selecting elements as in the case of t eordinary band filter, but also elements designed as set forth in the Hoyt patent to give an attenuation complemental to that of the main or toll transmission link.

Line 101 terminates at station X in a net. Nwhich simulates its impedance throughout the entire frequency range of the currents transmitted thcreover. A hybrid coil or balanced three-winding, transformer serves to connect line 101 to incoming and outgoin channels-107 and 108, respectively. Channe 108 is provided with transformers 109,619;

109 passes outgoing currents from line 101 I to a low pass filter which selects those of frequencies below 200 cycles and transmits them to line 103. High pass filter 113 readily transmits currents of all frequencies higher than 200 cycles to transformer 110 which supplies them to a band filter having a transmis sion range extending fram'200 to 400 cycles. This band filter impresses its selected band upon. frequency changer 120 which is of the same general type as the element illustrated at Fig. 20 of the article *Ca'rner current telephony and telegraphy by Messrs. Colpltts and Blackwell, published in the Transactions of the American Institute of Electrical Enrent's for use withthe'frequency changer 120 in reducing the frequencies of the outgoing bandtransmitted thereby. Frequency changer 120 decreases the frequency of each component-of the transmitted subband by 200' cycles. This decreased frequency subband is then'selected by a band filter 133 having a plifier a so having a high resistanceelement in its space current circuit to circuit 131 from whichtuned circuits 132 select 200cycle 'curtransmission range from 0-to 200 cycles and is impressed upon outgoing line 104.' Currents transmitted over line 1'04are supplied at station Y. o a frequency changer 140, which increases the frequency of the received subbandby. 200 cycles, and this increased frequency subband is then selected by a band filter 150 and after amplification is impressed upon incoming channel 151 i b frequency changing operation of the device 140 is accomplished by combining the components of the received subband with 200 c cle waves supplied by tuned circuits 141.t rough an amplifier.

- Circuit 106 .isused to'transmit cycles base frequency current from station X to the remote station Y. This current is selected by a low pass filter 143 and is supplied to a harmonic reproducer 144 of any desired type which supplies harmonic frequency currents which it is transmitted to line 102.. T e 100.

to its output circuit 145. The harmonic rea the output circuit of the second electric discharge device and a consequent generation of harmonics thereof. .In order to increase the distorting action of the second electric discharge device, it is provided with a high resistance in series with space current source. The distorted base frequency wave comprismg the various harmonics in the output'cir- 9111i; of the second eiectric discharge device is impressed upon the input circuit of a three-- element electric discharge device which serves to amplify the harmonics and supply them to circuit 145.

In a similar manner currents originating in line 102 are separated into various frequency subbands each of 200 cycles extent and each subband is reduced to the range of 0 to 200 cycles before transmission to station X. After reception at station X, it is again restored to its original frequency position. It is of course to be understood that the frequency range of the currents transmitted over each individual cable will be determined by the circumstances. Moreover,

certain portions of the speech frequency spectrum may be discarded, as in the system of Fig. 1 of application Serial No. 537,156 (Patent 1,565,091) of which this application is a division.

Circuit 106 is associated at station Y with a band pass filter 160 which transmits cur rents of a narrow band of frequencies including 200 cycles. This circuit serves therefore to transmit back from station Y to station X a return control frequency wave, the amplitude of which at station X will be subject to the same transmission conditionsas affect the various message subbands. In accordance with the invention, this 200 cycle wave 'is selected from circuit 106 at station by band pass filter 170, identical ter 160, and after selection and amplification is impressed upon' again control device 171 which is associated with amplifier, 172 to regulate the gain or amplification of the subband incoming over line 103. Similar gain control devices 178, 179, 180, etc. are associated with amplifiers 173, 17 1, 17 5, etc., to regulate the gain or amplificationof the subbands incoming over the other cable circuits.

In the gain control system illustrated, the input circuit 17 7 is associated with the gain control devices 171, 178, 179, 180, etc., one for each of the transmission circuits 103, 104, 105, etc. The gain control device 171 includes a three-element electric discharge device 190 and a resistance network. This network comprises resistances 192 and 193, each of very high magnitude, as of the order of a half megohm, and resistance 19 in shunt thereto, and a capacity element 195 which serves as a low impedance for all alternating currents to divert them from the resistance paths. Space current passes mainly by way of resistance .194 which may be of a few thousand ohms to match the internal space current resistance of the device 190. Resistance 193 is of such magnitude as to effectively separate the input circuit of amplifier 172 and the output circuit of gain control element 190 so far as alternating current is concerned. The only action of device 190 will therefore be to impress a direct current E. M. F. across resistance 192. The resistance 192 is included in the polarizing grid-cathode circuit of am in character with filplifier 172 in such a manner that the difference of potential caused by the flow of space current therethrough tends to oppose the polarizing source 196. The result is that the grid potential of amplifier 172 may at times be only sli htly negative or even positive and the ampli yingaction of the device 17 2 will be large. As the energy received over circuit 177 increases, the space current of device 190 falls and likewise the potential difference across resistance 192- The grid of amplifier 172 therefore becomes more negative and the amplifying action of this amplifier decreases, thus compensating for the increased transmission on circuit 103.

At station Y the gain control device 200 is associated with the input circuit 176 of the harmonic reproducerl i so as to be controlled by the base frequency wave of 100 cycles frequency transmitted from station X. This gain control device functions in a manner similar to the device 171, described above, to control the amplifying factorof amplifier 188 associated with the'circuit 103. Similar gain control devices, illustrated schematically in the drawing, are associated with the input circuit 176 to control the gain or amplification of the subbands incoming over circuits 104. 105, etc.

The transmission of the base frequency current from station to station Y serves a double function in that it enables the frequency change at station Y to be made exactly the converse of that at station X, and that it serves to determine the operation of the gain control apparatus.

Alt-hon h the invention has been disclosed as embodied in certain specific arrangements,

the principles of the invention are obviously is subject to variations, an electric discharge device associated with said line, a pilot line associated with said transmission line, and means for utilizing a wave on said pilot line varied in accordance with said attenuation variations to gradually and continuously vary the amplifying factor of said electric dischargIe device.

3. n a system of transmission regulation, a transmission line the attenuation of which is subject to variations, a pilot line the attenuation of which varies in the same manner as that of said transmission line, a threeelement electric discharge device associated with said line, asource of grid potential for said discharge device, and means to impress upon the grid circuit of said device an opposing electro-motive force from said pilot line which varies gradually and continuously in accordance with the attenuation variationsof said transmission line.

4. In combination, a two-wire transmission line carrying currents for transmission in opposite directions, means for supplying currents of different frequencies thereto, said line having such impedance as to considerably attenuate said currents, a pilot line carrying alternating currents the attenuation of which varies in the same manner as that of said transmission line, amplifiers connected to said transmission line, and means under the control of said current transmitted over said pilot line for causing the amplifying factor of said amplifiers to vary gradually in such manner as to compensate for the attenuation of said transmission line.

5. In combination, a pilot conductor, a three-element electric discharge device having an input circuit connected to said conductor and a space current circuit including a resistance element, a transmission line subject to attenuation variations of the same kind as those to which said pilot conductor is subject, an amplifier connected to said transmission line having a cathode, an anode and an impedance control element, and means connecting said resistance element in circuit with said cathode and impedance control element to impress a polarizing electro-motive force therebetween and thereby control the amplifying factor of said amplifier.

6. In a system of transmission regulation, a plurality of transmission lines subject to attenuation variations, a pilot line subject to the same attenuation variations as said transmission lines, an amplifier associated with each end of each of said transmission lines, and means under the control of current transmitted over said pilot line for causing the amplification of said amplifiers to vary gradually in such manner as to compensate for the attenuation variations of the associated transmission line.

7 In a gain control system means for transmitting a current over a pilot channel in one direction to determine the gain necessary at the receiving terminal and means for transmitting current of a different character over said pilot channel in the opposite direction to determine the gain necessary at the trans mitting terminal. v

8. In a system of transmission regulation, a transmission line subject to attenuation variations, an amplifier associated with one end of said transmission line to control the currents transmitted in one direction, an amplifier associated with the opposite end of the line to control the currents transmitted in the opposite direction, a pilot line, and means at each end of said transmission line controlled by currents transmitted over said pilot line for effecting gain control of said amplifiers. 9. In combination, a transmission llne,

means for transmittin currents from opposite ends of said line, said line having such impedance .as to considerably attenuate the and means for obtaining a source of potential independently of the waves amplified by said device which varies gradually and continuously solely in accordance with the attenuation variations of said transmission line to bias the grid element of said discharge device. I

11. In a system of transmission regulation,

a transmission line subject to attenuation variations, a three-element electric discharge device for amplifying the waves on said line, means for deriving a wave independently of the waves amplified by said discharge device having attenuation variations corresponding solely to the attenuation variations of said transmission line, and means for rectifying the derived wave for obtaining a potential to bias the grid of said discharge device and vary the amplifying factor of said electric discharge device.

In witness whereof, I hereunto subscribe my name this 27th day of July, A. D., 1925.

'ELMER V. GRIGGS. 

